In the automotive industry two significant systems are utilized in the painting of automobiles. One topcoat system which utilizes thermoplastic resins is known as the acrylic lacquer system. In this system the base polymers are the homopolymers of methyl methacrylate and copolymers of methyl methacrylate and acrylic acid, methacrylic acid, alkyl esters of acrylic acid or methacrylic acid, vinyl acetate, acrylonitrile, styrene and the like. The acrylic lacquer topcoats have been acknolwedged to have outstanding aesthetic properities. Another outstanding topcoat system used in the automotive industry is the thermosetting acrylic resins as described in U.S. Pat. No. 3,375,227, issued Mar. 26, 1968.
These topcoat systems have outstanding chemical resistance, outstanding resistance to cracking and crazing among other outstanding properties, but to the expert paint formulator, the thermosetting acrylic resins have not, in the past, quite provided the aesthetic properties obtained in the acrylic lacquer systems. In these systems a pigmented base coat composition is applied to the metal substrate to hide metallic blemishes and provide the aesthetically pleasing colors desired followed by the application of an unpigmented layer of polymer which imparts a "deep" color appeatance to the base coat and durability to this pigmented base coat. This system, however, is not without its problems. Aesthetic quality of the coating is totally dependent on the application of the base coat. The clear topcoat magnifies any weakness in this base coat including the highlighting of any color deficiencies of the base coat. The clear coat also acts as a magnifying mirror for ultraviolet radiation which can accelerate rather than retard any degradation of the base coat due to exposure to ultraviolet radiation. In addition, many of these coating systems in use today utilize metal particles in the base coat to provide an aesthetically pleasing metallic appearance. Note U.S. Pat. No. 3,639,147. However, problems have occurred with the use of metallic pigments resulting in color loss in the base coat.
In order to overcome the deficiencies of the metallic pigments, pearlescent pigments have been considered for use in the base coat, either with or in place of conventional pigments. Note commonly assigned, copending U.S. patent applications Ser. No. 440,764 filed Nov. 1, 1982 and Ser. No. 518,583 filed July 29, 1983. In order to produce novel and improved color effects iron oxide encapsulated mica particles have also been used in a transparent topcoat in a multilayer system. Note commonly assigned; copending U.S. patent application Ser. No. 526,724 filed Aug. 26, 1983, now U.S. Pat. No. 4,499,143.
Accordingly, what is needed in this art are improved coating compositions and coating systems which are aesthetically pleasing as well as durable and easy to control.